Decision making: effects of methylphenidate on temporal discounting in nonhuman primates

Decisions are often made based on which option will result in the largest reward. When given a choice between a smaller but immediate reward and a larger delayed reward, however, humans and animals often choose the smaller, an effect known as temporal discounting. Dopamine (DA) neurotransmission is central to reward processing and encodes delayed reward value. Impulsivity, the tendency to act without forethought, is associated with excessive discounting of rewards, which has been documented in patients with attention deficit hyperactivity disorder (ADHD). Both impulsivity and temporal discounting are linked to the dopaminergic system. Methylphenidate (MPH), which blocks the DA transporter and increases extracellular levels of DA in the basal ganglia and prefrontal cortex, is a primary treatment for ADHD and, at low doses, ameliorates impulsivity in both humans and animals. This study tested the hypothesis that low doses of MPH would decrease the discounting rate of rhesus monkeys performing an intertemporal choice task, suggesting a reduction in impulsivity. The results support this hypothesis and provide further evidence for the role of DA in temporal discounting and impulsive behavior.